Method for reduction of interference from harmonics



June 16, 1925. 1,542,525

L. J. RICH METHOD FOR REDUCTION OF INTERFERENCE FROM HARMONICS Filed Jan. 26, 1921 3] noentoz 61 (Emma,

Patented June 16, 1925.

UNITED STATES,

. LESTER J'. RICH, 0F WASHINGTOIN', DISTRICT OF COLUMBIA.

METHOD FOR REDUCTION OF INTERFERENCE FROM HARMONICS.

Application filed January 26, 1921. Serial No. 440,180.

T 0 all whom it may concern:

Be it known that I, LESTER J. R1011, a

citizen of the United States of America, re-

siding at \Vashington, in the District of Columbia, have invented a certain new and useful Method for Reduction of Interference from Harmonics, of which the following is a specification.

The present invention has reference to improvements in method of producing telegraphic signals, being applicable to systems using alternating or periodic currents, of either radio frequency or audio frequency.

Prefatorily, stations operated by means of alternating currents send forth signals carried by currents or waves of a given frequency, known in the art as fundamental frequency, and in addition, send forth currents 0r waves of other frequencies known in the art as harmonics The frequencies of the harmonics are integral multiples of the fundamental frequency. The useful energy is represented by the current or wave of fundamental frequency. The harmonics are produced by unavoidable imperfections in the generator or oscillator used to supply alternating current and are a form of waste product, being of no use or assistance in the production, transmission or reception of signals. To the contrary, they are in detriment and constitute a nuisance since by them, interference is had with and some times wholly prevents the duplex or multiplex operation of the system, and because they interfere with the reception of signals at other stations in the vicinity. For in the present state of the art as practiced, when the current or fundamental frequency is started, stopped, or varied in any manner, to produce the dots and (lashes of the conventional or other type of telegraphic code, all the harmonics are started, stopped, or varied in a like manner. It is this variation of the harmonics which causes the interference with other signaling being carried on over the same or neighboring systems. The harmonic which does not vary but maintains a stead sustained note does not interfere with ot er signaling unless it be extraordinarily intense. The most desirable method of dealing with harmonics would be to suppress them entirely if this were possible; the next best method 1s to so devise the sending apparatus that the harmonics give a steady sustained note instead of one which varies with every change of the fundamental.

By my invention I am enabled to produce a method whereby the last named process of dealing with harmonics may be carried out, that is, a method whereby the current of fundamental frequency may be started, stopped, or varied in intensity to form the dots and dashes of a telegraphic code without changing appreciably any of the harmonies.

In order that the invention and its mode of applicationmay be readily understood by persons skilled in the art, I have in the accompanying illustrative drawings and in the following detailed description based thereon, set out what I believe to be pre ferred embodiments of my invention.

In these drawings, I have shown a diagrammatic view of a possible embodiment of my invention.

Having more particular reference to the drawings, in connection with which like characters of reference will designate corresponding parts throughout the several views:

E designates a source of alternating current of a given fundamental frequency which for convenience, will be referred to as f Due to unavoidable imperfections, harmonics of frequency 2, 3, 4, etc. will also be generated at E. R R and R indicate resistances. while L indicates a self inductance. and C and O condensers. A key K is to be used in formingthe signals of the Morse or other telegraphic codes and electrical conductors 1 and 2 are provided and have connection with the remainder of the system (not included in the diagram) which, according to the particular case, may be a telegraph line. cable, antenna, earth, or some piece of electrical apparatus. The various individual parts are. of course, connected by conductors in the sequenceindicated in the diagram, so as to form an arrangement often designated in the art as a Wheatstone bridge. The inductance L will have associated with it a certain amount of resistance,which for convenience may be referred to by the symbol R The manner in which this apparatus performs its functions is as follows: If the inductance L and the capacity C are so chosen that and if the resistances R R and R are so balanced for any of the harmonics.

chosen that the products R R and R are R are equal, then itis a property of the Wheatstone bridge that an electro-motive force at E having a frequency 7 will cause no current to flow in the conductors 1 and 2, and the Wheatstone bridge is said to be balanced for the frequency f. Now if the key K is depressed, the condenser C is connected in parallel with the condenser O and will produce the same effect as increasing the capacity of C so that the relation 21rf= Um rents of corresponding frequencies in con ductors 1 and 2 and whatever may be connected thereto, regardless of whether the key K is depressed or not. While depressing the key K causes a slight change in the magnitude and phase of the harmonics in conductors 1 and 2, by properly selecting L and C, this change may be made so small as to be beyond apprehension. For accomplishing this, L should be made comparatively large with a correspondingly small value for C. For the same reason, C should be no larger than necessary to give good signals, preferably, C should be from one-fourth to one-twentieth as large as C.

While the above is offered as a practical example of this invention, it is to be understood that the invention is to be viewed in a broader sense than that set forth, and that the apparatus described above, While illustrating a possible and practical embodiment, chosen for the purposes of illustration, there are other more or less similar embodiments of the invention capable of accomplishing the same object in substantially the same manner; and that in a more generalized form the invention may be described as follows:

A Wheatstone bridge is arranged with the input in one of the two conjugate arms and with the output connected to the other;

the four remaining arms consisting of impedances (not necessarily the particular combination of resistances, inductances and condensers described hereinbefore); these impedances being so selected, that the bridge is balanced for the fundamental frequency. A key is connected to the bridge so that by depressing it, the bridge is thrown out of balance for the fundamental frequency, but is not appreciably altered in its ability to convey (currents of twice or more than twice the fundamental frequency.

An apparatus such as last outlined will, obviously, accomplish the desired ends and will permit of signaling with currents of the fundamental frequency without appreciably changing the harmonics. The harmonics will give a steady sustained note during signaling with the fundamental frequency,

thus, greatly diminishing their interference with other contemporary signaling on the same or neighboring systems.

I claim:

1.. In an apparatus used for the production of alternating current signals, a VVheatstone bridge interronnecting the source of alternating current and the like, means operable to balance or unbalance said bridge for the fundamental frequency of the source to transmit signals to the line.

2. In an apparatus used for the production of alternating current signals, a Wheatstone bridge interconnecting the source of alternating current and the like, means operable to balance or unbalance said bridge for the fundamental frequency of the source to transmit signals to the line, said bridge being unbalanced for a large proportion of the harmonics of the fundamental frequency at all times.

3. In an apparatus used for the production of alternating current, a line, a plurality of impedances connecting the source to the line, said impedances being interconnected to form a Wheatstone bridge between the source and the line, and means for changing one of the impedances of the Wheatstone bridge to change the current flowing through the line.

4. The method of producing telegraphic signals in a transmission line from an alternating current source which consists in alternately balancing and unbalancing a Wheatstone bridge for the fundamental frequency of the source.

LESTER J. RICH. 

